In a thin, flat display device such as a liquid crystal display or an organic electroluminescent (EL) display, thin film transistors (TFT) using amorphous silicon or polycrystalline silicon for the material of a channel is used for a picture element driving device. In the meantime, as for a display device using an organic EL device, trials to use TFT using organic molecules for a driver circuit are widely made so as to reduce a manufacturing cost and realize a display device provided with flexibility.
In TFT using so-called low-molecular-weight organic molecules for a channel, in most cases, a vacuum-deposited film including pentacene is used. In the meantime, for a polymer, various molecules such as P3HT or F8T2 are used.
Generally, in case an organic molecules are used for a channel, a problem that the performance of FET is slow occurs. This reason is that the mobility of a carrier conducting in a channel is low, even single crystal pentacene the most mobility of which has been observed is two order of magnitude smaller than polysilicon, and the mobility is at most similar to amorphous silicon. In the case of polymers, the mobility is further two order of magnitude smaller than that of pentacene.
To improve such a problem, various techniques are proposed; however, in the case of low-molecular-weight organic molecules, it is general to use a single crystal for a channel and an evaporated film is often used. In the case of polymers, it is general to orient molecules in a direction parallel to a channel and various techniques for it are proposed. For example, in a patent document 1 (JP-A No. 115805/2004), to increase the orientation of molecules in a channel, molecules which have a photoalignment property are adopted as a polymer insulator used for a gate insulating film. Besides, as in a non-patent document 1 (Journal of Applied Physics, Vol. 80, 431, (1996)) for example, orientation by rubbing is also representative technique.
Recently, in addition to polymers, trials to use nanowires for a channel of TFT are made. For example, in the non-patent document 1, FET using silicon nanowires for a channel is produced. To make mobility of carriers higher, nanowires are oriented in a direction parallel to a channel as in the case of polymers. For example, in the case of a non-patent document 2 (Nature, Vol. 425, 275, (2003)), the orientation of wires randomly oriented on a surface of a solvent encircled by four plates is aligned in parallel with two plates by narrowing an interval between the opposite two plates as in a method of forming Langmuir-Blodgett films and the wire is bonded on a substrate.
As described above, techniques for increasing carrier mobility to enhance the performance of organic TFT have been developed. In most, the orientation of organic molecules forming a channel is enhanced to reduce the scattering of carriers in the channel. In TFT using semiconductor nanowire for a channel, technique for enhancing the orientation of nanowires for the similar purpose is also used.
However, the above-mentioned prior art has a problem from a viewpoint of the compatibility of the cost and the productivity requested from a practical viewpoint. For example, as vacuum evaporation used in manufacturing a thin film of low-molecular-weight organics requires a vacuum though the vacuum evaporation has an advantage that the thin film having high carrier mobility can be easily formed, it is disadvantageous in the cost and the productivity. Besides, the orientation of polymers and nanowires cannot be enhanced so much by reforming a surface on which a channel is formed or by rubbing, and carrier mobility cannot be enhanced to a required extent.
Propositions except these techniques also have a problem that the cost and the productivity cannot be also made compatible or enough orientation cannot be acquired.
For an advantage in using TFT using an organic molecule or nanowire for a channel for a display device, the display device has flexibility and in addition, it is low-priced. Therefore, there is a problem that even if TFT can be manufactured at a low price, the display device cannot be driven or that even if the display device can be driven, a TFT manufacturing cost is high.